Allergic Conditions

Allergic conditions and allergic reactions occur when the immune system misidentifies harmless foreign substances-called allergens-and reacts to them as if they were harmful. Learn about common allergens such as food and insect stings.

These allergens can cause different types of allergies and related conditions that affect different parts of the body. In this section, learn about the most common allergic conditions and what types of allergens typically cause them.